GLUTATHIONE DEPLETION IN HUMAN ERYTHROCYTES AND RAT-LIVER - A STUDY ON THE INTERPLAY BETWEEN BIOACTIVATION AND INACTIVATION FUNCTIONS OF LIVER AND BLOOD

The interplay between bioactivation and inactivation functions of huma n erythrocytes and rat liver was studied. Glutathione depletion was us ed as a measure of the amount of reduced glutathione (GSH)-reactive co mpound. Iodoacetamide (IAcA), N-ethylmaleimide (NEM) and diethyl malea te (DEM), which are electrophiles that need no metabolic activation, w ere able to deplete GSH in incubations with either aqueous GSH solutio n or erythrocytes. These results indicate that these compounds can pas s the erythrocyte membrane. Cyclophosphamide (CP), 3-hydroxyacetanilid e (3-HAA) and 2-methylfurane (2-MF) needed metabolic activation by rat liver microsomes to deplete glutathione in incubations with aqueous G SH solution or erythrocytes. By measuring the sum of both reduced and oxidized glutathione [=total glutathione (GT)] it became clear that GS H-reactive metabolites are generated out of CP, 3-HAA and 2-MF by the action of microsomes and that these metabolites can pass through the e rythrocyte membrane. As GT depletion was higher when microsomes of phe nobarbital-pretreated rats were used, the metabolites were (are expect ed to be) generated by phenobarbital-inducible enzymes. GT was also de pleted in incubations with haemolysate and 3-HAA or 2-MF but not in in cubations with aqueous GSH solution, which indicates that erythrocyte cytosol can metabolize 3-HAA and 2-MF into GSH-reactive compounds. The pesticides monuron and monulinuron did not affect GT concentrations w hen aqueous GSH solution, haemolysate or erythrocytes with or without microsomal activating system were tested. When hepatocytes were incuba ted with 3-HAA or CP (2 mM), about 2 mM of internal GT concentration w as depleted. The hepatocytes excreted GSH-reactive metabolites generat ed from 3-HAA and CP (about 20% of the metabolites formed for 3-HAA). Erythrocyte GT was not depleted in co-incubations of hepatocytes and e rythrocytes with 3-HAA. This can be explained by the amounts of GSH-re active metabolites excreted by the hepatocytes, which would require ve ry effective uptake by the erythrocytes in order to be detectable. Cop yright (C) 1996 Elsevier Science Ltd